1. Field of the Invention
This invention relates to polarization-insensitive optical switch apparatus, polarization-insensitive optical multiplexing apparatus, and interferometric multimode fiber optic apparatus in which the indices of refraction of various beam paths through portions thereof can be varied with respect to that of other portions. Accordingly, it is the general object of this invention to provide new and improved apparatus of such character.
2. Description of the Prior Art
Polarization-insensitive switching of multimode fibers has been achieved by means of mechanical switches which move an input fiber into alignment with two output fibers, at two stable positions.
Electronic carrier multiplexing of two optical signals has been accomplished. Usually, the multiplexing stage is performed electronically; the resulting signal modulates the current through a light source. The drive currents of two different light sources can be modulated, and the two signal carrying fibers can be combined into a single communication fiber by means of a fiber combiner.
Disadvantageously, mechanical switching is slow, is power consuming, is usually operated at high voltages, is cumbersome, and is unreliable.
Disadvantageously, the multiplexing techniques (in which a single light source is modulated by the already multiplexed signal) requires very high linearity of the modulated source in order to prevent crosstalk. The light sources used in communication systems have nonuniform, nonlinear responses, sufficient to make this method inapplicable in many cases.
The modulation of the drive currents of two different light sources, utilizing an optical combiner, disadvantageously has at least a 50%, or 3 dB, loss due to the principle of combination of two light beams. Typical losses described in the literature are approximately 4 dB.